Green fabrication and biofunctional evaluation of C-phycocyanin/WPI-zein nanocomplexes obtained by the pH-shifting method.

Cyanobacterium Desertifilum tharense UAM-C/S02 produces C-phycocyanin (C-PC), a natural pigment-protein complex with high antioxidant activity, whose stability is affected by environmental and gastrointestinal conditions. C-PC was encapsulated in whey protein isolate-zein (C-PC/WPI-zein) nanoparticles using a green pH-shifting method. A 23 full-factorial design optimized the concentrations of zein, WPI, and C-PC. The optimal formulation (1 mg/mL zein, 10 mg/mL WPI, and 0.5 mg/mL C-PC) produced nanometric, relatively low polydisperse particles (156.1 ± 5.7 nm; PDI 0.234 ± 0.04) with high production (96.8%) and encapsulation efficiency (68.0%). AFM and TEM revealed a zein-rich hydrophobic core coated by soluble whey and C-PC proteins, while FTIR and DSC confirmed hydrophobic and electrostatic interactions driving self-assembly. Encapsulation significantly enhanced antioxidant activity and preserved functionality after simulated gastrointestinal digestion. These results demonstrate that C-PC/WPI-zein nanocomplexes are promising food-grade colloidal carriers for improving the stability and bioactivity of natural pigments in functional food applications.